The invention relates to improved protection methods for delicate or fragile, sharp-pointed materials; and more particularly to improved grinding and polishing method, equipment, and materials.
While the invention has many applications in protecting, e.g., jewelry, contact or impact sensitive and delicate parts or instruments, this invention relates more particularly to improved grinding and polishing applications, often with chemicals to help the planarizationxe2x80x94hence the name chemical-mechanical polishing (CMP).
The CMP method of surface planarization is a dominant technology in polishing glass. It also meets planarization requirements in the  less than 0.35 xcexcm (micron) feature sized multi-level devices and interconnects in the semiconductor industry. The CMP method is a preferred technology to carry out global planarization for various integrated circuits (IC). Planarized surfaces have become key to the success of advanced semiconductor devices and circuits, particularly for high-density multi-level interconnects.
In IC manufacturing, CMP involves competing requirements at various length scalesxe2x80x94e.g., uniform removal at the wafer scale, but non-uniform removal of protruding surfaces or areas to achieve planarization at the feature scale. The process, developed so far through trial-and-error, involves a synergistic interaction of many factors: fluid flow, fluid chemistry, slurry particle material, surface dissolution, and wafer material.
Ideally, the grinding and polishing method and equipment should provide: high uniformity and selectivity, low defect levels, high removal rate, low-pressure/high-speed capability, short product development time, and low cost. Also, the solid grinding/polishing abrasive materials should always remain as sharp as possible (always sharp), efficient, long-lasting, and low in initial and operating costs for rapid, reproducible grinding and polishing operations.
Grinding, polishing, or planarizing is widely used in many industries such as automotive, electronics, optical, machinery, metallurgical, medical, and glass. The quality and performance of an automobile, electronic components, optical instruments, precision machinery, glass plate, metallurgical material, or biomedical samples often critically depend on the cost and quality, e.g., flatness, surface finish, and reproducibility, of the planarized material. A perfectly planarized sample is often not available, too costly, or even impossible to obtain.
Making a modern 0.25 xcexcm CMOS IC chip requires 13 planarizing steps. A single major defect in any one step can result in the rejection of the entire chip lot. Even if each planarizing step has a yield of 99%, the final product yield loss from the 13 planarizing steps alone is over 12.2%. Raising yields from 99% to 99.5% in the planarizing steps still incurs a planarizing loss of 6.3%. This is still a big production and financial loss.
A planarizing machine is often used to obtain a planar, smooth outer surface on a material. The prior-art grinding or polishing machine often comprises a rotating wheel for mounting the material thereon. A colloidal liquid or liquid abrasive suspension is provided to wet the wheel and to hold/mount the material against the rotating wheel. The liquid suspension comprises a liquid suspension medium and a plurality of abrasive solid particles suspended therein. The liquid suspension is fed onto the wheel to chemically and mechanically grind or polish off surface layers of the mounted material. Both manual and automatic planarizing machines have been known in the art for quite some time.
But these machines are not satisfactory in many respects. The liquid suspension is costly but it is not reproducible; has short shelf lives; deteriorates in performance during use, transit, or even storage; and does not reliably produce quality product results. The solid abrasive particles wear out rapidly degrading the planarizing results. The solid abrasive particles also often agglomerate or break up into smaller pieces. Changes in particle size alone lead to loss of control of the desired surface finish. A large size distribution of abrasive particles produces a wide variety of surface finishes of differing smoothness and qualities, hampering product yield and reproducibility.
The hard, sharp, and brittle working edges or points on the solid abrasive particles are easily damaged, producing products of variable quality even during the same planarizing run. Damaged or worn-out particles always give inferior results. The planarizing process is inefficient. The process is also costly and nonreproducible.
A method of improving a planarizing process comprises: providing an ever-present protective or cushioning layer all around each solid abrasive particle to prevent its direct contact with its neighbors or with another solid object. The protective or cushioning layer preserves the critical tiny, rigid, sharp but brittle working edges or points on these solid particles. This can be achieved simply by selecting a liquid suspension medium having a density nearly equal to that of the solid abrasive particles. Improved equipment and a new planarizing suspension containing the special solid abrasive particles for practicing the new planarizing method are also disclosed.
To overcome the foregoing and other difficulties, the general object of this invention is to protect small abrasive particles, delicate parts, components, jewelry, or even small instruments from damage during their preparation, use, transit, and storage;
Another object of the invention is to provide an improved method to minimize damage on the working quality of a planarizing medium;
Yet another object of the invention is to provide an improved planarizing medium that is not only highly effective but longer-lasting;
It is another object of the invention to provide improved planarized surface finishes, rapidly and at low cost;
Yet another object is to provide a planarizing suspension in which the solid abrasive particles are practically forever sharp prior to use;
A further object is to greatly improve the material use efficiency of the solid abrasive particles in the planarizing operations.
Various other objects and advantages, and a more complete understanding of the invention, will become apparent to those skilled in the art from the following description and claims, taken in conjunction with the accompanying drawings.